1. Field of the Invention
The present invention relates to modulating digital communications, and more particularly to infrared (IR) communications and a controller for handling a multiplicity of modulation protocols used with IR signal systems.
2. Problem to be Solved
The most ubiquitous application of infrared (IR) signal systems to date has been the remote controller for home appliances, but IR signals are now being adapted for many other applications such as computer communications. An Infrared Data Access Standard committee (IRDA) has been formed to enhance interoperability among various vendor's products. The IRDA recommended standard utilizes a Universal Asynchronous Receiver/Transmitter (UART) in order to achieve low cost infrared communication with SDLC type of communication protocols. Since this standard is implemented with a UART, there are various problems associated with it by virtue of the asynchronous design. Two such problems are the bus throughput bottleneck and the overhead associated with asynchronous communication schemes. UARTs have been typically integrated into existing systems using interrupts to initiate the transfer of data to and from the system. The system latency in responding to these interrupt requests generates a bottleneck which limits the data throughput. Also, although the standard UART can run at baud rates up to 115.2 Kbps, the effective throughput is actually much less due to the overhead associated with asynchronous transfers. Consequently, the maximum data rate is not adequate for applications which transfer large amounts of data. Further, because the standard implementation only supports Hewlett-Packards' style of modulation, it is restricted in its application to only devices which follow that standard.
The use of a single UART poses another problem for IR systems since application programs usually access the UART directly leaving no space to intercept the data. For many existing IR communication programs, some intervention is necessary to adjust for the fact that the UART is being used for infrared rather than in a typical hardwired environment.
A further problem in this art is that existing multiprotocol communication controllers can run at only one type of modulation scheme at a time. Consequently, while waiting for an incoming signal, the controller is set to accept only one type of signal. This results in a loss of initial frames when a different type of signal is received until the incoming modulation scheme is detected and the controller is switched to the appropriate demodulator. While this is not serious as long as the communication protocol is set to deal with such problems, in the case of applications that do not take into account the fact that a UART is being used for IR communication, a missing first byte could be a critical problem.
The present invention is directed to solving the problems described above and provides an automatic modulation detection and handling scheme which can be implemented in an IR controller having an architecture designed to achieve solutions for these problems.